Thursday, December 23, 2010

Transport Nexus III: I Brought My Heart to San Francisco

San Francisco as seen from the ISS
Truth to be told, in all but the narrowest technical sense (driving the car) she brought me; it was my wife Paula's inspiration and effort that got us here. In any case the move and settling-in process account for the lack of posts here in the last couple of weeks, but now RM is up and running again.

In itself all this has nothing at all to do with space travel, but it does inspire some further thoughts about space stations. Recent discussion threads have included noteworthy heresies on this point.

In the traditional understanding that we all grew up on, an orbital station had two primary functions. One was to serve as a center for orbital operations such as communications, weather observation, and so forth; the other was to serve as a transport nexus, the meeting point between shuttles coming up from the surface and deep space craft arriving from other worlds.

Time and technology spoiled the first of these. All the observation and communications relay functions that Clarke and Heinlein expected space stations to perform are instead done by a host of satellites, and no crews are needed to change burned-out vacuum tubes.

The comment thread heretics challenged the second function as well. For a long time to come, spacecraft (or the modules that make them up) will be built and serviced on the ground, where the industrial infrastructure is. Work on orbit will be limited to final assembly, requiring no large staff of orbital workers. Deep space ships may well arrive and depart from individual parking orbits, with no need and no advantage to matching orbits with a big fixed orbital facility.

Space stations, in short, may have become obsolete before any had been built. The ISS, so far as I can tell, serves exactly none of the traditional functions of a space station. For practical purposes it is not a space station at all but a sort of training ship for future deep space missions.


Being obsolete is, in a surprising number of cases, no bar to success. San Francisco was technologically obsolescent from the very beginning of its history as a major city.

From a pre-industrial perspective it is the logical location for a seaport, a transhipment point between oceangoing ships and craft serving the vast inland waterway formed by San Francisco Bay and its outliers, which in turn provides access to rich agricultural regions: the wine country, Santa Clara (now Silicon) Valley, above all the Central Valley.

The railroad era - already well established by 1849 - changed all that, at any rate in principle. San Francisco, at the end of a rugged peninsula some 60 km long, is not a convenient rail terminus (except from the south). The original transcontinental railroad had its western terminus far inland at Sacramento, accessible to water transport; the line was later extended to Oakland, accessible to seagoing ships. And indeed Oakland eventually did supplant San Francisco as a seaport, though it took more than a hundred years, and the physical transformation of port facilities by the container revolution, to accomplish it.

What Oakland has not yet managed to supplant is Gertrude Stein, whose quip, "there's no there there," is practically her sole claim to fame. (Along with Alice B. Toklas brownies.)

San Francisco did not become a suburb of Oakland because of a combination of local circumstances and sheer inertia. Steamboats long remained more economical for regional transport around the Bay Area, and railroads were expensive to build so far from existing industrial centers. By the time these factors changed, San Francisco was already a major port, and network effects took over. It had infrastructure and port services, and the availability of these more than made up for the potential freight charge differential for east-west rail traffic.

Even when the port finally declined a broader network effect continued. In the current era San Francisco is, functionally, the downtown core of the Bay Area metropolitan region, accounting for about a tenth of the regional population but a much larger proportion of metropolitan services. These services to and beyond the region have only an incidental connection its original function as a seaport.


Unfortunately for space stations, the particular circumstances that allowed San Francisco to grow as a port even in the railroad era do not seem to apply in space. On the other hand, cities have always been defined less by their initial primary functions than by the secondary and tertiary services that they are uniquely suited to provide. If - for whatever reason - there are a large number of people in Earth's orbital space, they will probably aggregate in ways that allow them to have lunch together without having to undertake space missions just to get to a restaurant.

Where people go, cities will probably follow.



The image of San Francisco and environs was taken from the ISS.

237 comments:

«Oldest   ‹Older   201 – 237 of 237
Tony said...

Rick:

"My antigravity description does sound a great deal like buoyancy, but that's not really the analogy I have in mind. My mental metaphor is a machine that ratchets its way up the side of the gravity well (the problem being what it clamps onto)."

In hydrodynamics, you can achieve neutral buoyancy in a static equilibrium. (Well, not really, but close enough.) There is no equivalent static field similar to water (that we know of, anyway) in which to obtain buoyancy against gravity. All models of gravity, classic and quantum, require you to either be in an orbit or to constantly apply outward thrust in order to remain in dynamic equilibrium within a gravitation field. There is no static equilibrium.

Geoffrey S H said...

@Tony

So even if we get the correct materials for such a structure, its impractical due to a basic law of physics?
So when Clarke et al mention such a concept, they are handwaving the fact that it is impossible as aconcpet (given that there is no way we could send something down and up at the same time)?

Apologies if that sounds paranoid.

As regards AG, I saw in that flagship magazine for soft-science fiction, "New Scientist" a plan for a machine that can elevate biological organisms. Thinking that this could push them to the deck of a spacecraft, I filed it under "possible developement if one hand waves enough". If anyone wantstoknow more it was the experiment that could elevate mice into the air. Supposedly.
Thus, no hover tanks (but if we could manipulate gravity, surely just pulling something down/ towards the mechanism woud be no real replacement for the weheel? The further away the reaction mass (the planet) the less effective the device, so no fancy Ag launch vehicles either.

They predicted atomic toasters when the first reactors went online. Surprise surprse, we don't have them (or need them) now.

Tony said...

Geoffrey S H:

"So even if we get the correct materials for such a structure, its impractical due to a basic law of physics?
So when Clarke et al mention such a concept, they are handwaving the fact that it is impossible as aconcpet (given that there is no way we could send something down and up at the same time)?"


Rotating tethers don't violate any laws of physics. But they do violate the laws of practicality, unless you can arrange to balance the masses being sent up and down. What is handwaved are the technical problems to be solved (somewhat) and an economic environment in which cargo from Earth could be balanced by cargo from space (absolutely).

Attaching masses at both ends of the tether simultaneously is a bit of technical issue, but balancing every up payload with a similar mass down payload is a matter of tidiness. As long as you balance up and down traffic over short enough periods of time, the tether will wander up and down in orbit, and spin slower or faster, but it won't become unusable.

The real issue is that what is your down cargo made of, and why does it have an economic value on Earth? That is gratuitously handwaved, with various combinations of McGuffinite.

"As regards AG, I saw in that flagship magazine for soft-science fiction, "New Scientist" a plan for a machine that can elevate biological organisms."

That's electromagnetic levitation, not anitgravity.

Milo said...

Geoffrey S H:

"They predicted atomic toasters when the first reactors went online. Surprise surprse, we don't have them (or need them) now."

Technically, we do have nuclear-powered toasters. Toasters get their energy from wall outlets, which ultimately derive their current from (in some places) nuclear power plants.

Early authors just failed to account for economies of scale. It's easier, cheaper, and safer to have all our toasters powered by one big nuclear power plant, than to have miniature nuclear power plants installed in every toaster. (Indeed, fission technology hasn't been miniaturized enough for the latter to be possible at all, and likely never will be. Even if it were possible, it still wouldn't be a good idea due to aforementioned economies of scale.) Nonetheless, the availability of nuclear power has in fact helped us operate toasters. The same stuff is still being done, just not in quite the same place.

tsz52 said...

Tony:-

"Men of vision given the reins? Scientists and engineers are told what to do? Economists told to "keep up"? The people, offstage, not even a factor, except (presumably) that they do what their leaders tell them is best?

Santayana was right..."

Eek!: No no no no no - please understand that that is antithetical to what I am suggesting (it was brevity coupled with being built upon statements that I have already made about equalitarian division of competing power/ideology).

My entire setting is built upon a humanistic and direct-democratic renaissance devoted to never repeating the horrors of history (particularly the 20th and 21st Centuries [as I predict the 21st will be... only a sliver away from being the Century to End All Centuries]).

This entire age is considered the most reviled Dark Age in history: 'The Age of the Élites' or more colloquially 'The Age of the ****'.

The main purpose of moving into space is as a partial cure to the ailing of the human spirit; the theorist/engineer competition is a dynamic cross-pollenation (division of labour at its best) but in the brainstorm phase it is best to let theorists be as untrammelled as possible.

[Again being brief, since working with limitations often spurs greater creativity than blank pieces of paper do.]

In fact, any such project should be opened up to the public in this phase (particularly), since there's a good chance that the single greatest stroke of genius, elegance or beauty might come from some random dude, or child, somewhere.

If the economists and managers can be enthusiastic and innovative from the beginning then cool - if not, then they're (professionally) kept in a box until needed later on.

Aim high, pare down, then keep pushing and competing; rather than let an oversimplified model dictate what is 'possible' from the very beginning (which leads to shoddy crap rather than the stars).

tsz52 said...

[I'm having a hell of a time here posting this damn comment....]

Thucydides: [Please see above and:] I think that we actually agree more than disagree in terms of what we'd like our space futures to be - I just have far less faith in human nature than you seem to, so would have a different approach to reaching and maintaining the goal.

I think that my main point is that I hate hypocrisy and am a huge fan of coherence... far too much contemporary ideology will do everything to avoid addressing (or even acknowledging) the Ishmael Effect* at its very core: a libertarian ideology shouldn't just apply to small guys struggling away at the bottom, but should also extend to the very top: You need ideologies that compete with libertarianism too, in order to be libertarian.

So, just as you separate Church and State, you also separate Business and 'State'; and Science and 'State'; and Business and Science; and Business and Education; and Business and Media; and Business and Art; and Media and Art... etc for every bloc of power; you don't have them all more or less on the same side against 'the citizenry'.

[State and citizenry are in inverted commas because they are partly all of the above blocs.]

Dynamic equilibrium, uncompromisingly enforced: of course, I have dealt with the Ishmael Effect that resides here too, but this is a post, not my novel.

*Ishmael Effect: A statement that invalidates/contradicts its own premiss, eg: 'There is no such thing as objective truth' (is 'it is an objective truth that there is no such thing as objective truth'); or 'All morality is a cultural construct, so no culture should interfere with another's morality-derived actions' (is 'Except for the meta-morality... cough... that you shouldn't interfere with another culture's...').

Term derived from 'Moby Dick''s epilogue by Ishmael. [See also peritrope.]

Geoffrey S H said...

Blogger ate my post. Anyone get it?

As regards your system, Tsz52, the British ministry of defence could do with something like that........

tsz52 said...

Thucydides: [Please see above and:] I think that we actually agree more than disagree in terms of what we'd like our space futures to be - I just have far less faith in human nature than you seem to, so would have a different approach to reaching and maintaining the goal.

I think that my main point is that I hate hypocrisy and am a huge fan of coherence... far too much contemporary ideology will do everything to avoid addressing (or even acknowledging) the Ishmael Effect* at its very core: a libertarian ideology shouldn't just apply to small guys struggling away at the bottom, but should also extend to the very top: You need ideologies that compete with libertarianism too, in order to be libertarian.

So, just as you separate Church and State, you also separate Business and 'State'; and Science and 'State'; and Business and Science; and Business and Education; and Business and Media; and Business and Art; and Media and Art... etc for every bloc of power; you don't have them all more or less on the same side against 'the citizenry'.

[State and citizenry are in inverted commas because they are partly all of the above blocs.]

Dynamic equilibrium, uncompromisingly enforced: of course, I have dealt with the Ishmael Effect that resides here too, but this is a post, not my novel.

*Ishmael Effect: A statement that invalidates/contradicts its own premiss, eg: 'There is no such thing as objective truth' (is 'it is an objective truth that there is no such thing as objective truth'); or 'All morality is a cultural construct, so no culture should interfere with another's morality-derived actions' (is 'Except for the meta-morality... cough... that you shouldn't interfere with another culture's...').

Term derived from 'Moby Dick''s epilogue by Ishmael. [See also peritrope.]

tsz52 said...

Well my clarifying post to Thucydides seems to have finally been made to happen - sorry Rick if there's a deluge of dupes tomorrow....

Geoffrey S H:-

As it happens, my design approach is pretty much based on doing exactly the opposite of what we Brits tend to do, particularly re military systems and grand projects (SA-80 being about the best example)... which would pretty much embody the approach that Tony thought that I meant: Of course a bunch of rich aristocrats with no field experience know what's best - no need to consult the grunts... and no need to learn from history (re CIWS on the new ships... and retiring the carriers/Harriers as if '82 never happened...).

Re: EM levitation: As I understand it, the problem is that it only works with a tight, localised field; you could use such a thing to push you onto the deck but even a slight step takes you out of the field.

You might be able to have the apparatus on rails above you, following you round, with you sticking to painted lines on the deck, or something... dunno.

I can try to point you towards a bit more info on it, if you want.

Thucydides said...

tsz52

Your posts are a bit confusing. Separation of business and state is one of the foundations of libertarian thought; eliminating "crony capitalism" where business can lobby the State for favours (including crushing their competition). Ethanol is a great example; it is pretty useless as a fuel additive (your fuel mileage is actually lowered by the addition of ethanol) it is corrosive and takes more energy to produce than is recovered by use as a fuel, yet growers get billions in subsidies, distorting crop selection to the point that consumer food prices rise. A business that can get subsides from the taxpayer is literally stealing from their competitors who don’t get subsidies, with the State holding the gun.

Still, economists, managers and others are needed to provide guidance and discipline to various endevours, otherwise the people who come up with ideas might not have access to the resources needed, or understand how to use resources in the most efficient manner. There is an entire sub ecosystem of financiers (ranging from love money through banks to venture capitalists and finally loan sharks) to fill every “niche” for people who need finance; if those people don’t find the best rate of return for their money, they will be out of business at best, or suffering broken kneecaps or worse…

With that sort of discipline on the money end, the idea people will need to be equally dedicated and disciplined with the resources they have borrowed or they too will be out of business (or worse).

Anonymous said...

Rick: your idea about an AG effect sounds interesting, but needs some tweeks. First, don't think of it as a piston or ratchet, but as a field that you expand or collapse; your ship floats on the field and the field pushes on the earth; second, you need to have a regenerative feedback into the field to compensate for entropy, this doesn't have to be large, just enough to balance losses from 'bleed' into the enviornment. Oh, and the field shape should be columner to improve effecency.

EM levitation: you could run a superconducting magnet the length of your ship, but the magnetic field will push back on the hull just as hard as it pushes on people. Also, intense magnetic fields will present other problems, such as interfering with electronics, for example. Most of those are engineering details, like power generation, heat management, structural design, materials, and a whole host of other issues; unless you aren't concerned with mass penalties or power generation issues, then just spinning your hab is a lot easier and cheaper.

Ferrell

Tony said...

tsz52:

"My entire setting is built upon a humanistic and direct-democratic renaissance devoted to never repeating the horrors of history (particularly the 20th and 21st Centuries [as I predict the 21st will be... only a sliver away from being the Century to End All Centuries])."

Humanistic? What do you do with the majority of the world's population that still believes in the Divine and His influence? Or were all the religious people conveniently killed off by the (yet to be described) horrors of the 21st Century? (I'm beginning to get an idea what you think those horrors must be, and why you're hesitant to describe them in any detail...)

Direct democracy? How does the average person, even if you assume that he has a college-equivalent education, know enough to make a rational decision on even 10% of the issues that the government of a modern technological society must deal with? Even in representative democracies, the representatives need large staffs of specialists to give them at least halfway decent advice on the issues.

Who gets to decide what the causes of the horrors-never-to-be-repeated were? What if somebody disagrees? What if the vote is close? Why does the 50% + 1 who believe one thing get to ignore what the 50% - 1 think? Why doesn't this immediately cause a schism that leads to a civil war? (I mean, if we're going to "devote" society to the result of the decision, this stuff is at least as serious as anything else that has caused civil wars in the past.)

Tony said...

Ferrell:

"Rick: your idea about an AG effect sounds interesting, but needs some tweeks. First, don't think of it as a piston or ratchet, but as a field that you expand or collapse; your ship floats on the field and the field pushes on the earth; second, you need to have a regenerative feedback into the field to compensate for entropy, this doesn't have to be large, just enough to balance losses from 'bleed' into the enviornment. Oh, and the field shape should be columner to improve effecency."

You can do that with negative matter. Problem is, where does the negative matter come from?

Thucydides said...

You can do that with negative matter. Problem is, where does the negative matter come from?

Positive thinking, of course :)

tsz52 said...

Tony: I've had a fair crack at dealing with such problems as 'the tyranny of the majority'; it was 'humanistic' not 'Humanist': it is of/for humans as they are (or I thought they were...) across their full spectrum; not some Modernist/Utopian 'human' 'ideal', and nothing conveniently disposed of, but:-

It's Rick's blog not mine, and this is firmly in politics-land now (the initial point was more general);

however:-

I did type out a long post to answer some of your questions (I hate to seem 'all mouth and no trousers', and admire your good natured pragmatism), which has been saved. If you're really interested:-

tsz52 at yahoo dot co dot the official political entity that you get when combining gb with northern ireland (two letters).

tsz52 said...

Ferrell:-

"EM levitation: you could run a superconducting magnet the length of your ship, but the magnetic field will push back on the hull just as hard as it pushes on people. Also, intense magnetic fields will present other problems, such as interfering with electronics, for example."

Would that really work? Could you point me towards any literature that you might have come across that points in this direction?

Most of my stuff is optronic, with electronic stuff being only the things that have to be, and they're outside the hull, so this would be perfect for my ships.

My 'good guys' have comfortable centrifugal g, so even the minimal cutters have habrings with 60m radius (and it's still nearer to 4 rpm than I'd like), then there's an envelope around that = Stupidly Big Ships TM.... :(

Geoffrey S H said...

Just some quick,. not very thought through comments (blogger gulped down my more sophisticated post). Basically, Em would allow "Ag" without hover tanks- so far as I know. I would love some material on the matter though, tsz52,
as it would be an interesting subject to have a look around!

Of course, pressure of the decks at 1g isn't a massive problem for me, given that it is an alternative for torch 1g craft, which would have the same problems anyway.

Rotational gravity cannot be performed under thrust, which is my main motivation for this.

As for space elevators and instability. if there is no counterweight going down- engnines at the top to counter moevm,ent as a paylaod goes up? Expensive, but if it were possible it might allow some loads to be sent up without a counter weight needed, if that were ever necessary.

Not brilliantly thought out, sorry. but the eating of my post pretty much forced me to cobble this together.

@tsz52

Do you have any nation states or other actors in your setting? just curious as to who your "good guys" are. :)

@ Milo. Agree with your points, but saying that any state could pick up the reins I would disagree with. Britain? No chance. That's not political by the way, just having read postwar history and contemperary news from the 1990's onwards. there is simply no industrial capability, political or public will, or financial muscle (let alone soft or hard power) to contribute in any reasonable way to a recovery effort on that scale. britain would be better served hunkering down and appealing for security and help from someone else.

Australia on the other hand...
the next 100 years for that country will be very interesting.

Milo said...

Geoffrey S H:

"Rotational gravity cannot be performed under thrust, which is my main motivation for this."

It can't? Should be fine as long as the thrust is of significantly smaller magnitude than the gravity you want (likely to be true unless you have torchships).

One approach is to apply the thrust parallel to the axis of rotation. Applying thrust in other directions requires some elaborate switching to make sure you keep thrusting in the right direction, but that doesn't sound like too much of an issue.


"Britain? No chance."

Okay. I just picked a well-known European nation without bothering with research. I'm sure there's SOMEWHERE in Europe that's doing well for itself.

Anonymous said...

tsz52 said:"Would that really work? Could you point me towards any literature that you might have come across that points in this direction?"

Try looking at the official NASA site and look up experiments with super conduction magnets and levitating frogs...check out the Popular Sciance site as well, the same subject. Hyrdogen has the odd property of being repelled by magnetic fields, so the water in your body will be repelled by magnetic fields; they just have to be very intense fields. I hope that helps.

Ferrell

Thucydides said...

"My entire setting is built upon a humanistic and direct-democratic renaissance

Direct democracy will not result in a renaissance, quite the opposite if the ancient philosophers are to be believed. My own screen namesake has detailed descriptions of how the Athenian ekklesia was undermined by the actions of demagogues who manipulated the population into voting for dangerous schemes.

Limited Republics have a much more stable lifespan, the Res Publica Roma and Serenìsima Repùblica Vèneta lasted over four hundred years (which suggests the United States is about halfway through its natural lifespan). Strong empires with bureaucratic or religious organs also can last for extended periods (Ancient Egypt and Chinese civilization are good examples of the trope).

Direct democracy tends to lead to the "war of all against all" as individuals band together in an attempt to save what they have and take from others before others can band together and take from them (if you cannot get enough allies, you will be outvoted quickly in a direct democracy).

So for enough stability to undertake long term projects, we have a limited palette of social and political organizations to choose from. If we are looking for a social and political model which encourages experimentation and risk taking, well the number of models to choose from shrinks pretty rapidly.

Geoffrey S H said...

@Milo.

Maybe Germany. Maybe...

For all the high living standards, Europe has less of a global reach in many areas than other parts of the world. The areas that they do are dminishing by the decade (in comparison to other major powers). It may turn out that eventually they are so outclassed that the will to look at and try and work in any other part of the world diminishes.

Thucydides said...

Europe on its own won't do, but perhaps the Anglosphere nations (sharing common language, customs and laws based on association with or being members of the British Empire) have the horsepower to do so.

Outside of the United States, there are Canada, Australia and the UK as "First World" nations with up to date industry, well educated populations and decent resource bases. India is a regional power and has the potential to become a superpower this century. Even the other Commonweath nations have the ability to offer some limited extra support (even if it takes the form of geographic presence at or near a communications or transport node).

A series of nations sharing common background and similar values has the potential to become the global power of the 21rst century and beyond. The fact that most espouse "Classical Liberal" principles such as individual rights, property rights and the Rule of Law to a much greater degree than other nations or groupings is a hopeful sign.

tsz52 said...

Ferrell: Cheers! I did look into it a while ago and nothing seemed very practical, but I'll go and have another mooch.

Thucydides: As always, the labels are lacking, but I've been very mindful of the problems of various political systems, and found ways to ameliorate them.

It isn't direct democracy as one would generally understand it, but it's about the nearest label... again, this is Rick's table not mine, and I will respect his wishes as our host.

Geoffrey S H: Nation states? Kind of... (more world-view/ideology based than national values)... see above.

Problem with thrust g is what do you do when in orbit? Tumbling pigeon doesn't work for my ships, but it might for yours.

Next time I get my relentless research mole head on, I'll delve into everything I can per Ferrell's guidance, re EM levitation, and dig out what I've read already, then point you towards the good stuff... but I'm driven and thorough, not quick, so don't hold your breath. :)

Geoffrey S H said...

@tsz52:

Thanks (I take ages with research too, so no worries)! As to the rotational thing- an entire craft with Em might in the long run bee better than an earlier craft with a rotational ring and a non-g section. Just a thought.

@Thucydides.

Some problems with that I think (though I wish it were accurate)….

Most Commonwealth countries see the organization as a cultural association. There is no will to work together more closely. Regional blocs are focused on more. It is perceived that the superpowers will dominate the century so much (again) that they will be wasting their time getting together to be influential.

As for Britain in this, most political parties see Europe as the best option (closer integration etc). Even if the Commonwealth offers better options (which I believe it does, it certainly has room for small nations, Singapore using the organization to good effect, for example) concerns about former imperial guilt/baggage and a widespread belief that Europe is the only option (and an unwillingness to risk anything) shut down any debate on the matter. Not to mention the fact that opposition parties are pro-Commonwealth, governments are very pro-EU (no problem with that, but the Commonwealth is pretty much ignored). If the Commonwealth starts acting as a more unified organization, Britain will not be a part of that.

Hopefully that’s not too political, I’ll avoid this completely in future.

Jim Baerg said...

Tony: "What Jim seems to be missing is that the transfer is made neither in the plane of the origin planet nor the plane of the destination planet. The transfer is made in a plane that intersects both the origin and destination planes at the points of departure and arrival, respectively..."

Actually no.

Consider an Earth to Mars trip that is done by a nearly Hohmann trajectory, ie: Mars at the end of the trip is 180° from Earth at the start of the trip, but a few Gm off the plane of Earth's orbit. The plane of any orbit has to pass through the sun, so your proposal would put the transfer orbit at 90° to both Earth's orbit & Mars' orbit, requiring deltaVs of over 30 km/s at each end. Something like my proposal of a plane change at the line of nodes is clearly far more economic. (I'll concede I haven't *proved* it is the actual optimum.)

Could you give a reasonably clear explanation of what you are thinking rather than making bald assertions that I'm wrong.

"Re: tethers
Spacecraft can't stay on the tether. They're just released into orbit. For conservation of momentum reasons, you would need to bring down as much mass as you sent up, preferably at the same time."

It's nice if you have lots of downbound cargo, but if you don't you can use either the electrodynamic tether idea or a high ISP low thrust drive to restore the momentum it donated to the upbound cargo. This makes the tether a way to use high efficiency drives like ion or vasimir to provide part of the surface to orbit deltaV. The tether does have to be much more massive than the individual cargo items that go up it & there has to be an interval between cargo items for the drive to restore the tether's momentum, but that still leaves it as a way to cut launch costs if there is enough traffic to justify the initial capital cost.

There are issues with the idea that need to be worked out & which may be show stoppers, eg: how hard is it to renedevous with the tether, but the point you raised is a non-problem.

Thucydides said...

Balancing the energies in a momentum transfer tether is not trivial. While the mass of the tether probably gives you the flexibility to stagger catching and releasing mass, rather than trying to time everything to happen at once, there will be other effects like vibrational modes (the tether twanging and vibrating like a guitar string as unbalanced catches and releases occur) wich will add costs and complexity.

The tether will not be like a piece of super strong dental floss hanging or spinning in orbit, but a very complex and expensive item with vibration dampers, engines, solar panels and control nodes strung along the length. The engineering and ongoing upkeep might be our "seed" nexus for a colony or city in space.

Tony said...

Jim Baerg:

"...so your proposal would put the transfer orbit at 90° to both Earth's orbit & Mars' orbit, requiring deltaVs of over 30 km/s at each end.

...

Could you give a reasonably clear explanation of what you are thinking rather than making bald assertions that I'm wrong."


I said precisely what I meant to say, and it is a sufficient, though minimal, description of the procedure. I'll try again, with a little bit more detail...

The problem is that only by the wildest of coincidence does an interplanetary transfer opportunity coincide with either the origin or destination body passing through the plane of the other's orbit at the right time. So a simple plane-change-and-go is rarely (if ever) in the cards. The next simplest and energy effcient solution is to make the transfer in an orbit independent of either the origin or destination body, but otherwise efficient.

If it helps you to visualize what I'm talking about:

1. Assume a hohmann transfer where the origin body is at the top of it's ascending arc (WRT the destination's orbit) at departure, and the destination body is at the top of it's ascending arc (WRT the origin's orbit) at arrival.

2. Draw a hohmann type transfer orbit between the two, as if they were in the same plane.

3. But they're not in the same plane, so tilt and otherwise adjust the transfer orbit until the sun is at one of it's foci, but the origin and destination bodies still intersect that orbit at the right times.

4. You may not actually get this to work without adopting a transfer orbit that isn't quite a perfect hohmann solution. Oh well. It's still the most efficient orbit, excluding all other considerations.

But of course there are other considerations, most importantly having to start in a departure orbit that is coplanar with the transfer orbit, and end in an arrival orbit that is likewise coplanar. That is why starting from the ground is generally the most efficient solution for any opportunity -- the transfer orbit is unique, and so is the departure orbit.

A transfer orbit in the described class requires no plane change whatsoever. All it requires is acceptance of a coplanar departure and arrival orbit. This isn't a big problem if you assume bringing everything up from the surface of the departure body anyway. But starting at close to the right latitude on the origin body helps somewhat, which is why we use Cape Canaveral rather than someplace else on the East Coast for a spaceport.

Tony said...

Jim Baerg:

"It's nice if you have lots of downbound cargo, but if you don't you can use either the electrodynamic tether idea or a high ISP low thrust drive to restore the momentum it donated to the upbound cargo. This makes the tether a way to use high efficiency drives like ion or vasimir to provide part of the surface to orbit deltaV."

Only if your unbalanced throughput is very low. And it would be interesting -- to make an understatement of ludicrous proportions -- to engineer both a large enough high-Isp propulsion installation and it's power source, capable of sufficiently affecting the orbit of such a massive artifact.

Geoffrey S H said...

Ludicrous that concept may be... but nonetheless I really like that idea...

Hmmm...

Rick said...

quite the opposite if the ancient philosophers are to be believed

Though you could make a case (or at any rate I could) that Greek philosophy, from Socrates on, was mostly one big whine by sophisticated members of the oligarchic class.

The Athenian experience in the Peloponnesian War seems to prove mainly that war psychology often leads to stupid results - a state of affairs that historical experience suggests may transcend political institutions.


On orbit plane changes, there seems to be a certain amount of talking past each other going on. So far as I can tell, both of the following propositions are true:

1) It is cheaper in delta v to launch into the optimum orbit from the ground than to make an inclination change at any later point.

2) For high ISP drives, for which Oberth boot is not a consideration, inclination change maneuvers can be very cheap relative to mission delta v, though not AS cheap as launching into an optimum orbit in the first place.

If I'm wrong on these two points, clarification is in order.

Tony said...

Rick:

"1) It is cheaper in delta v to launch into the optimum orbit from the ground than to make an inclination change at any later point."

Essentially correct, if you presume that your resources and industrial infrastructure are on the ground. The further you shift spaceflight infrastructure into space, the more you look for compromise orbits that are positioned best for the largest variety of cases.

"2) For high ISP drives, for which Oberth boot is not a consideration, inclination change maneuvers can be very cheap relative to mission delta v, though not AS cheap as launching into an optimum orbit in the first place."

The problem with high Isp drives is not fuel efficiency per se, but the amount of impulse you have to apply over a given amount of time. This is a fixed function of the maximum thrust of the drive element(s), given the available electrical power. If you want to get there as fast as possible with a given impulse per second, you want to avoid plane changing. Also, by the very nature of high Isp propulsion systems, one can't avoid making the plane change a component of thrust vector over a considerable amount of time, meaning you can never do it in the most efficient way possible. This increases the proportion of the impulse budget one has to devote to inclination change.

Tony said...

Trying again...

Orbital inclination changes with high Isp propulsion is less of a matter of fuel efficiency and more about impulse efficiency. With a high Isp drive, one has to deal with allocating a limited amount of thrust to various trajectory demands over time. If you want to optimize for travel time, you want to allocate as much thrust as possible to orbital velocity modification, and minimize the amount of thrust allocated to plane changing (eliminating it altogether, if possible). If plane changing can't be avoided, as with the Dawn probe, then you have to allocate more time to the mission, because you have to make the necessary orbital velocity changes no matter what you do, then add on the plane change maneuvering requirements.

Thucydides said...

The Athenian experience in the Peloponnesian War seems to prove mainly that war psychology often leads to stupid results - a state of affairs that historical experience suggests may transcend political institutions.

True enough, so far as that goes. the main point I was making is direct democracy has no real means to diffuse such stampedes, even a feudal King or Emperor needs to entice the nobility to join a war or crusade (mostly by offering a cut of the plunder, you can see monarchs like Agamemnon or Elizabeth Gloriana using this pretty explicitly). Limited Republics generally tend to go to war to protect their own interests, and in the ideal world would only need a Navy and Marines to go out and bash heads when needed (responding to the Barbary Pirates, for example).

Existential threats like the Ottoman empire sacking and occupying your trading ports or Imperial Japan destroying the fleet focus the minds and energies on the problem right away, notice how the consensus for military action tends to leak away as the problem takes more and more time and resources to solve, or once it really is solved?

Scott said...

@Tony: First, you have to get the reactor up there to test. Not many people are happy about the idea of launching an entire reactor.

Then, you have to get utterly reliable remote operating systems or a failure in the remotes will cause an overall failure. Or you have to get a dozen nuclear-trained individuals into orbit... Both of which are incredibly expensive, and increase the chances of failure. *Any* failed test in space is likely to scrap the project. The AH56 helicopter program was scrapped, at least in part, because of a failure of the TOW missile at the politician's demo/sales pitch.

You can't afford for the project to fail, but you can't afford to test it properly either.

I suppose this brings us to a better question: How do you get enough space-tech infrastructure up into orbit to make space stations worthwhile? Stations won't get built early on, because it's not cost-effective.

What technologies would have to exist to get factories out of the gravity well?

Tony said...

Scott:

"You can't afford for the project to fail, but you can't afford to test it properly either."

A communications satellite couldn't be tested until it was put in orbit. Neither, to mention the most notorious example, could the Shuttle heat shield (as an integrated technological unit) without putting the Shuttle in orbit, with men aboard. Let's not get carried away with thinking that space nuclear power systems will absolutely have to be tested to the level that naval reactors were in the lab prior to running a prototype in the operational environment. If the only way to have a test is to fly one and control it through telemetry*, then that's what we'll do.

*Which is essentially how space propulsion systems are controlled anyway; the astronauts are really just passengers during major propulsion events.

"What technologies would have to exist to get factories out of the gravity well?"

Technologies that would reduce or totally eliminate the perception that factories need to be moved into space. The problem with the industrialization of space is that people who advocate it -- even those who have worked in industry -- simply don't understand how complex modern technology is. We've been through this before. A viable industrial base for modern technology requires millions ofp eople and everything they need to live and work. If you could move that much into space, guess what? You don't need to move all of it into space, because space access would be so cheap that space civilization wouldn't care whether or not the industrial infrastructure was up there with them.

Thucydides said...

What technologies would have to exist to get factories out of the gravity well?

The real question is what technologies would have to exist to replace factories out of the gravity well. Assuming for the moment that there is a large presence in space and a need for manufactured goods and services, we first look at the environment.

Space is awash with energy, so devices which can harvest energy and convert it to usable forms are the first and foremost order of business.

Bootstrapping is hard; complex devices are rare and expensive due to the cost of bringing them from the gravity well of Earth. Second order of business is to simplify as much as possible. Items with multiple uses are also to be desired.

Space industry might be carried out by solar sails, which can be converted to solar mirrors on site, providing thermal energy concentrated to the point of being able to vapourize metals if need be from target asteroids. Vapour deposition is the common and accepted way of building bulk items (it is easy enough to vapourize materials with the mirror, directing the jet onto the cold surface is the main challenge). Higher order industry will resemble a distillery of sorts, with high temperature vapours being fed in one end and condensates coming out the other end (including alloys created by mixing vapour streams and complex hydrocarbons boiled and refined from the carbon compounds and ices)

Buildings and shelters are constructed from "bricks" or tiles cast from slag materials, or vapour deposition on the metal forms of large structures to provide strength, insulation and radiation protection. Materials can be alloyed or layered as desired. This technology can be used like 3D printers to create complex objects as well.

High end materials like computer chips, valves and other items will be imported from Earth, based on the ability to continue to make then faster and more cheaply than vapour deposition or 3D printing can.

As capabilities increase, more complex items can be made, leading to import substitution and internal economic growth.

Anonymous said...

Thucydides said:"Buildings and shelters are constructed from "bricks" or tiles cast from slag materials, or vapour deposition on the metal forms of large structures to provide strength, insulation and radiation protection. Materials can be alloyed or layered as desired. This technology can be used like 3D printers to create complex objects as well."
When I read this I got the mental image of a giant Xerox machine cranking out layers upon layers to create the Enterprise...:)
Seriously, we won't dismantal factories and ship them into orbit; we will build substitutes for use in orbit (or on planetary colonies), and whether we shift production from Earth or we simply just run dual systems, we will expand our industrial base to follow our colonists...

Ferrell

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